Lean condition troubleshooting

[kh2kairi]

Codes po171 and po174: lean condition in bank 1 and bank 2

 

Cleared it the first time it came on months ago and didn't come back until recently. Now it's almost a daily thing.

 

No symptoms other than variable idle. Some days it fine others it varies between 100 and 300 rpms. Truck will not stall though.

 

Cleaned MAF, IAC, Throttle body, and PCV.

 

Freeze frame data for po171:

Fuel system 1: CL

Fuel system 2: CL

Calc load %: 7.8

ECT (°C) :88

STFT B1 %:1.6

LTFT B1 %: 21.1

STFT B2 %: -1.6

LTFT B2 %: 20.3

MAP (kpa) :59

Engine rpm:1305

Vehicle speed (km/h) 45

MAF (g/s) :20.39

TPS % :12.9

 

Not entirely sure what any of those values are supposed to be so I'm really confused.

 

Any ideas?

[8.1HD/ALLISON]

Year? Make? Engine?

 

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[8.1HD/ALLISON]

I would start by checking fuel pressure. Check intake gaskets for leaks by using propane or choke cleaner.

 

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[kh2kairi]

I'm sorry. It was in my signature.

2000 chevy silverado 5.3

[8.1HD/ALLISON]

Ah my bad, i'm on tapatalk and can't see signatures on my phone

 

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[txab]

I would start by checking fuel pressure. Check intake gaskets for leaks by using propane or choke cleaner. Sent from my LGL86C using Tapatalk

+1

 

Also fuel filter

[kh2kairi]

I'm gonna buy a fuel pressure tester tomorrow to be sure but I really don't think it's fuel related. I've already changed the fuel filter somewhat recently, had the fuel injectors blown out and I doubt its the fuel pump being that the truck runs and starts like a champ.

[txab]

Diagnosis is a step by step process. You can rent pressure tester vs buying.

 

Leaking intake gaskets can cause this problem and is somewhat common with todays plastic intakes

[oldscsc]

Long term fuel trim is almost maxed out. At most, long and short term fuel trims should be a combined max of +/- 5%. Your pickup is over 20%. The computer normally stops about +/- 25% as that's the farthest extent it can adjust the A/F ratio.

 

You are getting unmetered air into the engine somehow. Suspect either a vacuum leak or leaking intake gaskets. Try a cylinder leakdown test to verify intake gaskets are leaking before tearing everything down.

[kh2kairi]

Jesus. Just my luck.

 

What's a cylinder test?

[oldscsc]

Jesus. Just my luck.

 

What's a cylinder test?

No worries. Its not that big of a deal.

 

A cylinder leakdown test is just hooking up an apparatus that measures leakage. That is, an air hose is hooked to the apparatus and the hose end of the setup is threaded into the spark plug hole. The two gauges will measure air pressure and percentage of leakage.

 

If you find the intake gaskets are leaking, its not a big deal. Just pull the manifold (you may want to look into knock sensor replacements while you have the manifold off if you plan to keep the truck for some period of time), and replace the gasket. Sounds nasty, but if you've got a day to do it, it isn't too bad.

[kh2kairi]

So I checked the fuel pressure. Ignition on key off, it shoots up to 55 and then drops to 50 and stays there. At idle it stays at 50. I sprayed around the intake gasket and nothing changed.

[gmtech4]

14 yrs old,change the intake gaskets ,knock sensors and its harness